1. Field of the Invention
The present invention relates to a polyester resin composition improved in impact resistance, particularly impact resistance at low temperatures while maintaining its mechanical properties such as strength, stiffness and the like.
2. Description of the Prior Art
Hitherto, there have been proposed many methods for improving the mechanical properties (e.g. impact resistance) of thermoplastic polyester resins. Among these, relatively excellent methods are those described in Japanese Patent Application Kokoku No. 58-47419 and EP-A2-0367219. The former method is a method of blending a polyester resin and an .alpha.-olefin/glycidyl methacrylate/vinyl acetate copolymer, and the latter one is a method of blending a polyester resin and a graft silicone rubber obtained by graft-polymerizing an epoxy group-containing vinyl monomer onto a polyorganosiloxane polymer.
However, resin compositions obtained by the method described in Japanese Patent Application Kokoku No. 58-47419 have a problem that the impact resistance in the vicinity of room temperature is excellent, but that an improvement in impact strength at a low temperature below 0.degree. C. is not sufficient, so that the range of application of the resin compositions is limited. Resin compositions obtained by the method described in EP-A2-0367219 have a problem that an improvement in impact strength is not sufficient, so that the appearance of molded products obtained therefrom is poor. The above resin compositions also have a problem that when they are put in wet heat conditions under pressure, mechanical properties become remarkably poor.